JP2000018360A - Ball screw with cage type holder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw with a cage type holder which can improve a torque performance by preventing the interference between the holder and a piece, the collision to a ball and the biting into the ball. SOLUTION: In the ball screw with a cage type holder, having the piece 60 for a ball circulation on a ball nut 30, and arranged the cage type holder 40, providing plural long holes extending to the axial direction for separating balls 50 in a periphery direction mutually and also holding rollingly on the periphery surface, between a screw shaft 20 and ball nut 30 screwed thereto through the ball 50, the gap A between the screw shaft 20 and a cage type holder 40 is set to smaller than the gap B between the piece 60 and the cage type holder 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved ball screw having a cage type cage.

[0002]

2. Description of the Related Art For example, in a normal ball screw without a retainer as shown in FIG. 10, a ball 50 has a ball screw groove 22 of a screw shaft 20, a ball screw groove 32 of a ball nut 30,
The balls are densely arranged in the ball circulation path 62 of the circulation top 60 in a state where the balls are in contact with each other, and when the individual balls roll, they move in opposite directions at the contact points between adjacent balls. For this reason, slippage occurs at the contact portion between the balls, so that free rolling of the balls is hindered by a so-called competition phenomenon, torque resistance increases, and torque unevenness occurs. Since torque unevenness due to such ball competition generally worsens in low-speed operation and swing operation, for example, in the case of a ball screw used in an electric discharge machine or a wire cutting machine that requires low-speed and swing operation, It becomes a problem. Further, in a machining center where contour controllability is regarded as important, it is extremely disliked because it causes disturbance in motor control.

As a countermeasure in such a case, it is necessary to avoid direct contact between the balls to eliminate the competition between the balls and to improve the torque performance. For example, a ball retainer H as shown in FIG. Ball screws are known. The retainer H is provided with a number of round holes H2 for rollingly holding a ball in a cylindrical member H1. The ball is rollably disposed in the round hole H2, and a screw shaft and a ball nut are provided. Is installed between Therefore, the balls do not contact each other, and the torque does not fluctuate due to the slip resistance between the balls as described above. However, the retainer H moves in the axial direction together with the ball nut as the screw shaft rotates in a usage mode in which the screw shaft rotates at a fixed position and the ball nut does not rotate (movement amount of the retainer). However, if the movement stroke of the ball nut is large, the retainer H will fall out of the spiral groove of the ball nut and the ball will fall off.

Accordingly, a ball screw with a cage-type cage having improved such a point is proposed in, for example, Japanese Utility Model Publication No. 2-5145. This cage-type retainer 40 is formed by forming a large number of substantially axially long holes 42 in a thin cylindrical body as shown in FIG. 12 which is loosely fitted between a screw shaft and a ball nut. The ball is provided in the elongated hole 42 so as to roll freely. On the other hand, the ball nut has a hole extending over two adjacent grooves of the ball screw groove 32 as in FIG. 10, and a ball circulation top 60 is fitted into the hole to form a ball passage. 62 are provided. The ball moves axially in the long hole 42 of the cage type retainer 40 while rolling along the ball screw groove,
By passing through the ball circulation path 62 of the ball circulation top 60, the ball circulation path 62 gets over the thread (land portion) of the screw shaft and repeats internal circulation. The long hole 42 of the retainer 40 has a length that allows the ball to move in the axial direction with respect to the retainer so as not to hinder the internal circulation of the ball. This ball screw with cage cage has the advantage that the torque fluctuation is small and the moving stroke of the ball nut is not restricted by the rolling ball.

[0005]

However, in the case of the conventional ball screw with cage type retainer, there is still room for improvement in the following points.

The top 60, which is a circulating component, is generally designed to have a dimensional relationship such that the inner diameter of the top protrudes toward the inner diameter of the ball nut in order to easily pick up the ball. For this reason, the cage-type retainer 40 arranged in the space between the screw shaft and the ball nut interferes with the inner diameter side of the frame 60, and the relative movement with respect to the ball nut sometimes lacks smoothness.

[0007] Even in electric discharge machines and wire cutting machines which perform machining at low speed and swinging operation, in order to improve work efficiency,
At times other than machining, high-speed feed operation is often performed. In this case, the ball circulating through the top 60 collides with the long hole 42 of the cage-type cage 40, and a dent is formed on the cage 40, and the torque characteristics may be deteriorated by the influence of the dent. .

The ball leaves the retainer 40,
When the ball slides over the land surface of the screw shaft and moves to the next groove, the ball moves away from the BCD (Ball Circle Dia) once by centrifugal force and returns to the BC again.
Draw a trajectory returning to D. Therefore, the ball is
When returning to the above, a strong collision with the retainer 40 or a phenomenon in which the ball is pinched between the nut and the retainer (a phenomenon of biting like a wedge) may occur.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the unsolved problem of such a conventional ball screw with a cage-type cage, and has been made in consideration of the relative dimensions in the radial direction of the cage-type cage.
By devising the hardness etc., the interference between the cage and the top
It is an object of the present invention to provide a ball screw with a cage-type cage having improved torque performance by preventing collision with a ball, biting of a ball, and the like.

[0010]

In order to achieve the above object, the invention according to claim 1 is directed to a screw shaft having a helical ball screw groove on the outer peripheral surface and a ball screw groove of the screw shaft. Internal ball nut having a ball screw groove formed on the inner peripheral surface thereof and a guide groove provided in a part of the ball screw groove so as to circulate the ball over the thread of the screw shaft to form a circulation path. And a number of balls that are rotatably fitted in the ball screw groove of the ball nut and the ball screw groove of the screw shaft, and are disposed in a space between the screw shaft and the ball nut. A ball screw with a cage-type retainer comprising a thin-walled cylindrical cage-type retainer provided with a plurality of long holes extending in an axial direction on a peripheral surface thereof so as to be spaced apart from each other and rotatably held therein. Screw shaft and the cable The gap between the mold holder was set smaller than the gap between the frame and the cage retainer.

According to a second aspect of the present invention, in the ball screw with a cage type retainer according to the first aspect of the present invention, the hardness of the cage type retainer is determined by changing the hardness of the heat-treated material (HRC).
22-30) and the hardness of the ball (HRC62
~ 67).

Further, according to a third aspect of the present invention, in the ball screw with a cage type retainer according to the first or second aspect of the invention, a magnetic force is applied to the cage type retainer.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 show one embodiment of a ball screw with a cage type retainer of the present invention.
2 is a front sectional view, FIG. 2 is a II-II sectional view thereof, FIG. 3 is a perspective view of a retainer, FIG. 4 is a perspective view of a circulation top, and FIG. 5 is an enlarged sectional view of a main part. First, the configuration will be described. The ball screw 10 has a screw shaft 20 having a helical ball screw groove 22 formed on an outer peripheral surface and a helical ball screw groove 32 corresponding to the ball screw groove 22 on the inner peripheral surface. The formed ball nut 30, a thin cylindrical cage-type cage (hereinafter simply referred to as a cage) 40 disposed in a space between the screw shaft 20 and the ball nut 30, a ball screw groove 22 of the screw shaft 20, and A large number of balls 5 interposed between the ball nut grooves 32 of the ball nut 30 and loosely fitted in the long holes 42 of the cage.
0 and a top 60 joined to a hole 36 provided in the ball nut 30.

As shown in FIG. 3, the retainer 40 has a thin cylindrical shape and has a plurality of axially extending long holes 42 penetrating the inner and outer surfaces on its peripheral surface. A columnar portion 44 is formed. The ball 50 has the ball screw grooves 22 and 3 of the screw shaft 20 and the ball nut 30, respectively.
2 and are rotatably separated from each other by engaging with the long holes 42 of the retainer 40. As shown in FIG. 4, the frame nut 60 straddles the two ball screw grooves 32 adjacent to the ball nut 30 and
Has a shape that fits into the through hole 36 formed in the body portion of the screw shaft 20, and has a deep surface on its inner peripheral surface that allows the ball 50 to climb over the thread between the ball screw grooves 22 of the screw shaft 20. A ball circulation path 62 is formed. The frame 60 is provided for the ball circuit on the right side in addition to the one for the ball circuit on the left side shown in FIG. The position of the right-hand frame is 90 ° out of phase with respect to the left-hand frame, and FIG. 1 shows one ball 5 passing through the right-hand frame.
0a is shown over the thread of the screw shaft.
The retainer 40 is rotatable relative to the ball nut 30 and is immovable in the axial direction by retaining rings 70 and 71 mounted on the inner peripheral surface of the ball nut 30.

As shown in FIG. 5, the retainer 40 disposed in the space between the screw shaft 20 and the ball nut 30 has a gap A between its outer diameter surface 43 and the inner diameter surface 63 of the top 60. There is a gap, and there is a gap B between the cage inner diameter surface 44 and the thread outer diameter surface 23 a of the thread land portion 23 of the screw shaft 20. Then, the size of the interval between these two gaps is set so that the interval A> the interval B.

Next, the operation of this embodiment will be described. The ball nut 30 is supported so as to be non-rotatable and movable in the axial direction, and the screw shaft 20 that is not movable in the axial direction is rotated clockwise as viewed from the right in FIG. Then, a large number of balls 50 fitted in the ball screw grooves 22 of the screw shaft 20 and the ball screw grooves 32 of the ball nut 30 roll along the ball screw grooves 22, and the ball nut 30 rotates the amount of rotation of the screw shaft 20. Moves to the right in the axial direction by a stroke proportional to. At this time, the ball 50 rolls along the ball screw grooves 22 and 32, but the retainer 40 is attached to the ball nut 30 by retaining rings 70 and 7.
1 so that the ball 50 rotates with the rolling of the ball 50, and the ball 50 is
2 is moved in the axial direction by the amount of the lead of the screw. Cage 40
The ball 50 that has moved to the front end side (the left end side in FIG. 1) is pushed by the columnar portion 44 of the retainer 40 and rides over the thread land portion 23 of the screw shaft 20 while being guided by the ball circulation path 62 of the top 60. The ball screw groove 22 adjacent to the next (right side in FIG. 1). During this circulation, the ball screw groove 22
32 are isolated from each other by slots 42 in retainer 40 and do not touch. Therefore, the rotation of the screw shaft 20 and the ball nut 3
The movement in the axial direction of 0 is very smooth, and there is almost no torque fluctuation. The ball 50 is connected to the screw shaft 20.
The retainer 40 does not move in the axial direction with respect to the ball nut 30 even if it circulates along the outer surface of the ball nut 3.
The movement stroke of 0 is not limited by the rolling of the ball, and a large stroke can be used.

Further, according to the present embodiment, the inner diameter surface 63 of the frame 60 fixed to the ball nut 30 and the retainer 4
0, the gap B between the thread outer diameter surface 23a of the screw shaft 20 and the inner diameter surface 44 of the retainer 40 is larger than the gap A between the outer diameter surface 43 and the screw shaft 20.
Is set smaller (A> B), even if the retainer 40 swings during rotation, the screw shaft 20 and the retainer 40 come into contact before the retainer 40 and the top 60 come into contact. Therefore, there is no possibility that the retainer 40 is caught on the top 60. Regarding the contact between the retainer 40 and the screw shaft 20, the thread outer diameter surface 23a of the screw shaft 20 is generally polished smoothly because it is used as a reference surface.
There is no problem with contact. Thus, a more stable and smooth operation of the ball screw without torque fluctuation can be obtained.

Next, another embodiment of the ball screw with a cage type retainer of the present invention will be described with reference to FIG. In this embodiment, the steel cage 40 is made of a material whose hardness is larger than that of the tempered material (HRCs 22 to 30) and smaller than that of the steel ball 50 (HRCs 62 to 67). It is manufactured so that the cage and the ball do not damage each other. In this way, by restricting the range of the hardness of the retainer 40, when the screw shaft 20 is rotated at high speed to feed the ball nut 30 at high speed, the retainer 4
Even if the ball collides vigorously with 0, no dent is formed on the retainer 40, so that the durability of the retainer 40 at the time of high-speed feeding can be ensured and the torque characteristics of the ball screw can be improved.
The regulation range of the hardness HRC22 to 67 of the cage is determined based on the results of experiments. That is, hardness HRC2
In the experiment using the steel cage 40 made of the tempered material of 2 to 30, dent scratches were found, whereas the quenched cage (hardness is approximately HRC50) showed no nick scratches. Was. From these results, the lower limit of the hardness of the cage type cage of the present invention was determined as HR
C22 was set. On the other hand, unless the hardness of the cage exceeds the hardness of the ball, HRC 62 to 67, the ball was not damaged.
Set to.

The other structures, operations and effects are the same as those of the first embodiment. 6 to 9 show still another embodiment of the ball screw with a cage type retainer of the present invention.

This embodiment is different from the first embodiment in that the cage 40 is made of a magnetized material. Examples of the magnetized material include the following. Hardened magnet (KS magnet steel), powder type magnet. For example, sintered magnets of alnico-based magnet powder, ferrite magnets using metal oxide powder, plastic magnets in which ferrite powder is mixed with flexible plastic, high magnetic conductivity alloys such as silicon steel and permalloy, Co-based and others Amorphous alloy.

Referring to FIG. 8, the operation of the present embodiment will be described in comparison with the case where the cage is not magnetized (FIG. 9). Generally, in a ball screw with cage type cage of a top circulation type, when the cage is not magnetized (FIG. 9), the ball 50 slides on the surface of the screw shaft 20 in the ball nut 30, When the ball 50 is viewed from the axial direction when moving to the adjacent groove via the circulation path 62, as shown in FIG. 9, each ball 50 is pressed against the inner wall of the ball circulation path 62 by the action of the centrifugal force as shown in FIG. , The trajectory of the ball is BC
D and once bulges outward (see line L in FIG. 7). When the ball has passed through the ball circulation path 62, a trajectory returning to the BCD is drawn again. When the ball returns to the long hole 42 of the retainer 40, the ball strongly hits the retainer and damages it. Alternatively, as shown in FIG. 9, the ball 50 traveling as indicated by the arrow mark m collides with the end wall surface of the ball circulation path 62 and receives a repulsive force in the k direction, and the retainer 40
And the ball 50 receives a repulsive force in the 1 direction, and the ball 50 is hard to return to the BCD.

On the other hand, in the case of the present embodiment (FIG. 8), when the ball 50 moving on the BCD passes through the ball circulation path 62,
Due to the magnetic force of the retainer 40, the cage 40 is pulled in the direction of arrow g against the centrifugal force. If the magnetic force exceeds the centrifugal force, the ball 50 moves in the direction of arrow h, that is, in the direction of BCD. Therefore, when returning to the long hole 42 of the retainer 40, the ball does not strongly collide with and damage the retainer. In addition, the end wall surface of the ball circulation path 62 and the cage 4
A phenomenon of receiving a strong repulsive force upon colliding with zero or being pinched like a wedge can be prevented, and a smooth operation can be obtained.

The ball screw with cage type retainer of the present invention may be one in which two or all of the first to third embodiments are incorporated. In the cage-type cage 40 of each of the above embodiments, the length of each of the plurality of long holes 42 is long from one end side to the other end side of the cage. , The length of each long hole can be divided in the axial direction (for example, divided into two) in accordance with the axial movement amount of the ball 50 of each ball circuit. Further, when divided in the axial direction in such a manner, the long holes before and after the axial direction may be arranged in a zigzag manner.

[0024]

As described above, according to the first aspect of the present invention, the clearance between the screw shaft and the cage type cage is set smaller than the clearance between the top and the cage type cage. It is possible to prevent the phenomenon that the relative motion to the ball nut of the cage loses smoothness due to interference with the top,
As a result, there is an effect that the torque performance of the ball screw with the cage type cage can be further improved.

According to the second aspect of the present invention, the hardness of the cage type cage is set to be larger than the hardness of the tempered material and smaller than the hardness of the ball. In high-speed feeding operation, the ball circulating through the spinner vigorously collides with the long hole of the cage type cage, and a dent is formed on the cage, and the torque characteristic is deteriorated by the influence of the dent. This can prevent such a phenomenon that the torque performance of the ball screw with the cage type cage can be further improved.

Further, according to the third aspect of the present invention, since the magnetic force is applied to the cage type cage, the ball is separated from the cage and passes through the circulation path of the circulating frame to the outside of the BCD, and is then held again. When returning to the container, it is possible to prevent the ball from strongly colliding with the retainer, or to prevent the ball from biting into the nut and the retainer, thereby improving the torque performance of the ball screw with the cage type retainer. This has the effect of being able to be further improved.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a perspective view of a cage type cage.

FIG. 4 is a perspective view of a circulation top.

FIG. 5 is an enlarged cross-sectional view illustrating a relationship between a cage, a top and a screw shaft.

FIG. 6 is a front schematic cross section of a main part for explaining a cage and a ball rolling locus according to another embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view perpendicular to the axis.

FIG. 8 is a schematic cross-sectional view illustrating the operation of a cage according to another embodiment of the present invention.

FIG. 9 is a schematic cross-sectional view illustrating the operation of a conventional cage.

FIG. 10 is a front sectional view of a conventional ball screw without a cage.

FIG. 11 is a perspective view of a conventional cage with holes.

FIG. 12 is a front view of a conventional cage type cage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ball screw 20 Screw shaft 22 Ball screw groove 30 Ball nut 32 Ball screw groove 40 Cage type cage 42 Slot 50 Ball 60 Top 62 Ball circulation path

Claims (3)

[Claims] 1. A screw shaft having a helical ball screw groove on an outer peripheral surface, a ball screw groove corresponding to the ball screw groove of the screw shaft on an inner peripheral surface, and a ball is formed on a part of the ball screw groove. An internal circulation type ball nut having a circulation path formed by providing a guide pin so as to circulate over the screw thread of the screw shaft, and freely rotatable between a ball screw groove of the ball nut and a ball screw groove of the screw shaft. Are arranged in the space between the screw shaft and the ball nut,
A cage-type cage having a thin-walled cylindrical cage-type cage provided with a plurality of long holes extending in the axial direction on the peripheral surface so as to be spaced apart from each other in the circumferential direction and to roll freely. A ball screw with a cage type cage, wherein a gap between the screw shaft and the cage type cage is set smaller than a gap between the top and the cage type cage. 2. The cage type cage according to claim 1, wherein the hardness of the cage is larger than the hardness of the tempered material (HRC22 to 30) and smaller than the hardness of the ball (HRC62 to 67). The ball screw with a cage type retainer according to claim 1. 3. The ball screw with a cage type retainer according to claim 1, wherein a magnetic force is applied to the cage type cage.